K2 Problems

[Brent Sutphin WB4X]

We had a storms in the area here yesterday. Afterwards my K2-100 would not
stay on.  When I turned it on, it came on for a few seconds then a high
current warning and then off.  Long story short I determined that the K2 rf
power transistors are bad.  I plan to order new ones tomorrow.  Question is,
do I need to look further?

Brent  WB4X

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[Don Wilhelm-4]

Brent,

If I were you, I would order 2 1N5711 diodes (PN E560004).

I suspect that your original problem is that KPA100 diodes D16 and D17
were damaged by static, with the result that the KPA100 output was at
maximum (150 t0 180 watts) no matter what the power setting. That
condition continued for long enough will place stress on the base K2 PA
transistors and they will die of overload.

I just  recently responded to a similar private enquiry, I copy my
response below..

Replace Q11 and Q13 since they also can be damaged as a secondary effect.
---------------------------------------------------------------------------------
If you did not try to transmit for long after you saw the HiCur display,
the base K2 PA transistors may still be OK.

Your main problem is that the KPA100 wattmeter diodes have either
shorted or opened, so the K2 can no longer determine power output. Since
the K2 MCU thinks there is zero power output, it increases drive to the
maximum - an external wattmeter will normally show 150 to 180 watts.  
That does place stress on the base K2 PA transistors which may fail as a
secondary effect.

If that describes your situation, replacement of KPA100 D16 and D17 may
normally set things in order again.

To prevent similar further incidents  make certain there is a good DC
path across the feedline of all your antennas.

"Other transceivers do not have this problem" will fall on deaf ears
here.  The "other transceivers" control power output only by changing
the drive to the final stages.  Elecraft products actually measure the
power at the output stage and control the power output by a closed
control loop.  That does require sensitive diodes at the output of the
PA, but it also means that those diodes are susceptible to static
charges on the antenna.

Static on the antenna can be caused by wind, rain, sleet, snow or nearby
lightning charges.
A 2 or 3 watt resistor with a value between 5000 ohms and 100k ohms
across each feedline will be a great help in reducing the number of
failures of KPA100 wattmeter diodes.
--------------------------------------------------------------------------------------------------

73,
Don W3FPR

On 8/23/2012 7:47 PM, Brent Sutphin wrote:

> We had a storms in the area here yesterday. Afterwards my K2-100 would not
> stay on.  When I turned it on, it came on for a few seconds then a high
> current warning and then off.  Long story short I determined that the K2 rf
> power transistors are bad.  I plan to order new ones tomorrow.  Question is,
> do I need to look further?
>
> Brent  WB4X
>
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[Bill Frantz]

I assume you want a non-inductive resistor in this application.

Cheers - Bill, AE6JV

On 8/23/12 at 17:49, [hidden email] (Don Wilhelm) wrote:

> A 2 or 3 watt resistor with a value between 5000 ohms and 100k ohms
> across each feedline will be a great help in reducing the number of
> failures of KPA100 wattmeter diodes.
-----------------------------------------------------------------------
Bill Frantz        | I like the farmers' market   | Periwinkle
[phone]      | because I can get fruits and | 16345 Englewood Ave
www.pwpconsult.com | vegetables without stickers. | Los Gatos, CA 95032

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[vk4tux]

I would probably go with 2 x 1.5KE51CA-ND inverse paralleled across the diode to avoid impedance issues.

[Don Wilhelm-4]

The answer may be in the antenna field.  If the SWR is in excess of
2.0:1, then the equipment will reduce power (foldback).

73,
Don
W3FPR

On 8/23/2012 10:45 PM, vk4tux wrote:

> I would probably go with 2 x 1.5KE51CA-ND inverse paralleled across the diode
> to avoid impedance issues.
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-Problems-tp7561545p7561555.html
> Sent from the Elecraft mailing list archive at Nabble.com.
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